The Legacies always did 45-46 mpg at m/way speeds - about what they did overall too. To be honest I was never aware of any regeneration going on.

The Yeti (VAG 2.0 CRD engine) did about 38 on the m/way. Regeneration happened every 1500 miles or so and, frankly, you couldn't miss it. The temperature gauge rose to near the red zone and it ran even rougher than usual. The instant mpg chnaged to c 15mpg for 5 minutes or so. All totally normal according to three dealers and Skoda UK.

Yaris d4d 64mpg.

but doesn't have all the expensive components now fitted to diesels.

Therein lies the extra expense with the Mazda 6 diesel in the OP's post....They're not renowned for their DPF reliability. I've done huge mileage in my petrol one with no probs at all.

My HDi Xantia is a bit old for valid comparison. Electronically controlled high pressure injection but no DPF. Mid to high forties on a ru

Car can be a pita occasionaly but apart from a valve failing in the injection circuit (ran rough but not grounded) and a lift pump fail (flatback to dealer) the fuelling system has been trouble free over 11yrs/140k.

C2 VTS 1.6HDi, keep it to 70 and it'll return over 60mpg, run it at 80 and it drops to about 50mpg, averages 53mpg local and town, it gets driven quickly but not high speed if that makes sense.

Toyota Hilux 3.0 Auto, now sold, motorway cruising about 30mpg, the manual is better say 32/33, but when people start claiming 37/38 mpg normal for a 2 ton brick and it's robust transmission?

The above was true on older diesels. Later ones are now a nightmare if just driven in town due to Euro V emmisions. Diesel Particulate Filters and associated controls cause all sorts of issues not least lunching engines with diesel contanimation of sump oil due to aborted regen cycles, expensive DPF replacements and future nightmare MOT tests.

2001 C220 CDI auto - 2.2 143cv - used to get 55+ between London and Manchester. High 40's the rest of the time i.e. around town. Best mpg was obtained when the car was run in i.e. > 100,000 miles.

2002 FIAT Marea estate - 1.9 105cv - still getting 5.4l/100km = 52mpg in old money. Just run in - 350,000km on the clock.

The benefit of a diesel is that they'll do well regardless of how they are driven - in town or with a heavy right foot, a petrol's mpg will drop rapidly, whereas most diesels are consistent day-in-day-out IF they get chance to warm up i.e. reasonable runs. Resale will be higher too.

Potential problems... there shouldn't really be any at such a low mileage.

2001 C220 CDI auto - 2.2 143cv - used to get 55+ between London and Manchester. High 40's the rest of the time i.e. around town. Best mpg was obtained when the car was run in i.e. > 100,000 miles.

2002 FIAT Marea estate - 1.9 105cv - still getting 5.4l/100km = 52mpg in old money. Just run in - 350,000km on the clock.

The benefit of a diesel is that they'll do well regardless of how they are driven - in town or with a heavy right foot, a petrol's mpg will drop rapidly, whereas most diesels are consistent day-in-day-out IF they get chance to warm up i.e. reasonable runs. Resale will be higher too.

Potential problems... there shouldn't really be any at such a low mileage.

Might have been true once but I find even that debatable, certainly not the case now with all the paraphenalia that has to be attached to remove the pollutanst and smog.

My preference is for a low pressure turbo petrol, seemless power throughout the whole rev range not the all or nothing delivery that blights most diesels.

Edited by Buster Cambelt on 25/10/2011 at 20:08

Most diesels have different gear ratios to their petrol equivalents so they're turning over at markedly lower rpm at a given speed which makes a big difference on motorways. I've had 65mpg from a 2000 5 speed Passat TDi driven lightly and at 65mph on the motorway during a fuel "crisis" and I now get 32 mpg from my 2011 Santa Fe 2.2 diesel auto at 75-80 mph. Some petrols like Toyota Avenis have high final gear ratios and are good at motorway speeds. I'd check what the Mazdas are set at and if the petrol is close go for that. If its a company car its got to be diesel.

I used to have a Peugeot 406 HDi Automatic which on mostly motorway driving would get around 46mpg which i thought was pretty good but plenty of HDi owners with manual gearboxes report 50+ without much effort even in general day to day driving.

This isnt a point about diesels in particular but i can report my S-Type 3.0 Auto petrol returned a genuine 34mpg on my recent trip to Portsmouth and back which i felt was impressive as its not like i was especially on an 'eco drive' with it.

Edited by jamie745 on 25/10/2011 at 00:24

My 330d Touring (245PS) 09 would regularly better 50mpg on a motorway run at or around the legal limit with 46 or 47mpg being easily obtainable, close to its overall average in my care. I don't recall the DPF ever regenerating and it used practically no oil in 23K miles.

My 07 A4 Avant 170PD struggled to better 40mpg, even driven like a mimser (below the legal limit) on the motorway it would only scrape 44mpg, it drank expensive oil (1/2l per 5k miles) and regenerated the smelly DPF often.

I think BMW make rather better engines than VAG....

My wife's 2.2 iCTDi Civic could easily manage more than 50mpg on a motorway run and used little oil, it didn't have a DPF but still managed Euro IV, a great example of a 4 cylinder diesel.

My conclusion is that manufacturers figues should be taken with a pinch of salt, cars vary but in fairness both my BMW and our Honda got very close to the manufacturers' claims, I'll refrain from commenting on the Audi.

Edited by idle_chatterer on 25/10/2011 at 15:32

With my Peugeot 806, 2000 , 100K miles, I return 40 mpg (7l per 100km) at french legal speed limits on motormays or 80mph.